For the elimination of the basic frequency of a mains disturbance it is generally known in the art to sum up successive samples picked up from a signal to be analyzed. The elimination of mains disturbances is generally effected by using digital filters which, however, can be of quite a complicated design and thus expensive, particularly depending on how much signal information is desired to be analyzed from the filtered signals. In certain special applications, for example when the signals to be analyzed are a kind of noise signals such as several bioelectrical signals like EEG and EMG, the only interesting quantity to be analyzed may be the amplitude of a signal, the above-mentioned digital filters often being unnecessarily complicated for the purpose.
An object of the invention is to provide a simple design and economic filter assembly for effectively filtering out all mains disturbances which is especially suitable for use when the only signal parameter of interest is amplitude or power. Other signal features, such as waveform or phase, are destroyed in the filtering process.